Z-Latent Heat Storage for Process Heat Applications.pdf

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Folie 1 >Latent Heat Storage for Process Heat Applications >J ochen Buschle

Latent Heat Storage for Process Heat Applications

J ochen BuschleDLR German Aerospace CenterInstitute of Technical Thermodynamics Stuttgart

Co-Authors: Wolf-Dieter Steinmann, Rainer Tamme

The Tenth International Conference on Thermal Energy Storage,Atlantic City, 31. May 2. June 2006


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Content

Presentation is presenting first results obtained in the national projectPROSPER dealing with industrial process steam storage.Possible contribution of Germany to planed new Annex 19.

Project partners are XELLA AG and SGL Technologies GmbHDuration 07/2004 06/2007

The project is funded by the Federal Ministry of Economy (BMWi) under

the contract FKZ 032736017

Latent heat steamstorage in process heat applications

Comparsion macro-encapsulation and external arrangement

Simulation results

Concepts to increase the power density of the storage

Conclusion


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Gas concrete manufacturing process

Hardening of gas concrete (steamatmosphere; max 13 bar)

Batch process, 2 cycles per day

155 kg steamat 13 bar for 1 m gas concrete = 100 kWhth

Xella Porenbeton GmbH (300.000 m/a corresponds to 30 GWhth/a)

weighing and mixing

hardeningcuttingbulking0

4

8

12

pressure[bar]

0 1 2 3 4 5 6 7 8 9 10

time [h]


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varying-pressure accumulator - Ruths storage

Charging pipe

Discharging pipe

Water feed pipe

Steam

Water

Pressure vessel


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Process description - State of the art

varying-pressure accumulators

2 Ruths steamaccumulators

70% of the required steamper cycle

is produced in the boiler

live steam;

70%

overflow;10%

Ruths-lowpressure;

15%

Ruths-high pressure; 5%

boiler autoclave 5-8 bar3-5 bar


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Potential for introducing latent heat steam storage

Isothermal steamaccumulators withPhase Change Material (PCM)

2 PCM enhanced steamaccumulators

(Tm = 152C and 171C)40% of the required steam per cycle isproduced in the boiler

live steam; 40%

overflow; 10%

Latent-high pressure;

25%

Latent-lowpressure; 25%

Latent heatstorage

Latent heatstorage

8 barboiler autoclave 5 bar


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Macro encapsulation

PCM Gas

Stiff encapsulation required

Definition of minimal gas volume inside capsules

Compensationof volume variation PCM

Avoidance of significantpressure variations

Gas volume requires about 20% of theinternal volume of the capsules


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External arrangement of PCM

PCM

Additional required:

Headers for the tube register

Unpressurised containment forthe PCM

Pump for circulation required


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Comparison macro encapsulation and external

arrangement

PCM steam

Boundary conditionstemperature step: 10 Kelvin

pipe diameter: 40 mm

heat transfer coefficient to the steam: neglected

thermal conductivity PCM: 0.5 W/mK

density PCM: 2000 kg/m

same amountof PCM


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Macro encapsulation vs. external arrangement

40

60

80

100

solidifiedPC

Mm

ass[%]

External arrangement

Macro encapsulation20

0

0 500 1000 1500 2000 2500 3000 3500

time [s]

External arrangementshows higher power level assuming the sameamountof pipe material


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Macro encapsulation vs. external arrangement

Outside pressure load demands higher wall thickness than inside

pressure load due to buckling

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

2 6 10 14 18 22 26 30

pressure [bar]

wallt

hick

ness[mm]

externally arranged PCM

encapsulated PCM

External arrangement

Macro encapsulation


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Comparison steam accumulator concepts

varying-pressure

accumulator

Macro-encapsulated

PCM

externally arranged

PCM

pressure vessel:

diameter: 1m; height: 3m; volume: 2.36 m; water level: 80%

PCM enhancement:

diameter tube: 4 cm; mass PCM: 1250 kg; thermal conductivity: 0,5 W/(m K)


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Simulation modell

ramp

I

Pump 1

true -1000Po...

5050


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Results simulation

1000 2000 3000 4000 5000

0

20

40

60

80

100

1000 2000 3000 4000 5000

0

1428

42

56

kW

time [s]

time [s]

Power

Provided heat

kWh


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Required thermal conductivity

0

200

400

600

800

1000

1200

0 5 10 15 20 25 30

k [W/mK]

time[sec.]

h = 100000 W/(mK)

h = 10000 W/(mK)

h = 1000 W/(mK)

thermal conductivity above 5 W / (m K) is advantageous


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Basic concepts to increase the power density of

thermal energy storage tested at DLR

Increase of the effectivethermal heat conductivity

Increase of the heat transfer area

PCM - Composite Integretion of fins


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PCM Composite

Solution: Compression of Saltand expanded graphite

Advantages expanded graphite:

Hight thermal conductivity

Corrosion resistance

material canbe machined


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Integration of Fins

Solution: Foils made of expandedgraphite

Advantages graphite foils:

Hight thermal conductivity(approx. 150 W/mK)

Corrosion resistance

Arrangement of foils verticalto the axis of the heattransfer pipes is optimal

with respectto theanisotropic heatconductivity of expandedgraphite

PCMPCM PCM

PCMPCM PCM

Graphite-foil

PCM

Steam pipe

10 mm

0,5 mm

Graphite-foil


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Lab scale experiments at DLR


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Conclusion

Isothermal energy storage is importantespecially for steamprocesses

External arrangementof PCM is advantageousThermal conductivity of 5 W / (m K) is required

Future work:

Lab scale experiment for validationof models

System simulation of gas concret production process with latent heatsteamaccumulator


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Thank You

for Your Attention


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Latent heat steam accumulator

Documents

Z-Latent Heat Storage for Process Heat Applications.pdf